Method of and apparatus for exciting luminescence in a cathode ray tube having an image screen composed of a material that is both cathodochromic and cathodoluminescent

ABSTRACT

Method of and apparatus for exciting luminescence in a cathode ray tube (CRT) having an image screen that is both cathodochromic and cathodoluminescent, whereby an electron beam effects luminescence of the image screen as well as writing upon the screen. Writing is accomplished at a high level of beam exposure and luminescence is accomplished at a low level of exposure.

[111 3,9d2fi96 [451 Aug. 26, 1975 1752.521 6/1956 lvcy 313/465 3.1482819/1964 250/549 X 1 1 METHOD OF AND APPARATUS FOR EXCITING LUMINESCENCEIN A Fyler........

3 560 782 2/1971 Hamann... 313/465 CATHODE RAY TUBE HAVING AN IMAGE3,631,295 12/1971 Poolcy 315/13 ST SCREEN COMPOSED OF A MATERIAL THAT ISBOTH CATI-IODOCI-IROMIC AND CATHODOLUMINESCENT PrimaryExaminer-Siegfried H. Grimm Attorney, Agent, or Firm-Arthur A. Smith,Jr; [75] Inventor. Lee T. Todd, Jr., Lexington, Ky. Robert Shaw; MartinM. Santa [73] Assignee: Massachusetts Institute of Technology,Cambridge, Mass.

Apr. 1, 1974 ABSTRACT [22] Filed:

[21] Appl No.: 457,112

Method of and apparatus for excltlng luminescence in a cathode ray tube(CRT) having an image screen that is both cathodochromic andcathodoluminescent, whereby an electron beam effects luminescence of theimage screen as well as writing upon the screen. Writing is accomplishedat a high level of beam exposure and luminescence is accomplished at alow level of exposure.

., Zw S/ 0 594 2 ,1 wqfmw 1 5 l 4 3 H %m "m 23 l 1 4/ W7T 3 95 M B U31 80 9 H R u i 3 m m n; uh. m mmD m a n 7 2 l 8 C WM k U .mF .H P 5 55References Cited UNITED STATES PATENTS 10 Claims, 3 Drawing FiguresMETHOD OF AND APPARATUS FOR EXCITING LUMINESCENCE IN A CATHODE RAY TUBEHAVING AN IMAGE SCREEN COMPOSED OF A MATERIAL THAT IS BOTHCATHODOCHROMIC AND CATHODOLUMINESCENT The invention described herein wasmade in the course of or under a grant from the National ScienceFoundation, an agency of the United States Government.

The present invention relates to a cathode ray tube whose image screenis both cathodochromic and cathodoluminescent and, in particular, to anovel way to excite the cathdoluminescence.

Attention is called to the following related applications being filedherewith and hereby incorporated herein by reference: Cathode Ray TubeWhose Image Screen ls Both Cathodochromic and Fluorescent and theMaterial for the Screen, Ser. No. 456,961, filed Apr. 1, 1974 (Todd, Jr.et al.); A Process for Preparing Cathodochromic Sodalite Having EnhancedColoration Properties and a Cathode Ray Tube Employing the Same Ser. No.456,962, filed Apr. 1, 1974; (Todd, Jr. et al.); and Cathode Ray TubeEmploying Faceplate-Deposited Cathodochromic Material and Electron BeamErase, Ser. No. 457,111, filed Apr. 1, 1974 (Todd, Jr. Attention iscalled also to the doctoral thesis of Lee T. Todd, Jr. (a copy of thethesis accompanies the application entitled A Process for PreparingCathodochromic Mixtures Having Enhanced Coloration Properties), whichthesis is hereby incorporated herein by reference; the work upon whichthe thesis is based was done by the inventor at MIT. The thesis containsan exhaustive list of references to prior work as well as detailedtheoretical analysis, neither of which is repeated here. The followingLetters Patent are made of record: US. Pat. Nos. 3,705,323 (Shidlovsky);3,598,750 (Phillips); 2,752,521 (Ivey); 2,761,846 (Medved); 3,706,845(Heyman et al.); 3,148,281 (Fyler).

Attention is called specifically to the application entitled Cathode RayTube Whose lmage Screen Is Both Cathodochromic And Fluorescent and theMaterial for the Screen wherein there is disclosed a screen materialthat can be caused to ltm inesce by the systems disclosed herein. Thescreen material there described is Na,,Al (Ge,,Si O 2( lz)NaX, wherein Xis chosen from the group consisting essentially of chlorine, bromine, OHand iodine and mixtures thereof, y varies from about 0.003 to 0.30, andz l. Whereas in the other application the mechanism for causingluminescence is ultraviolet radiation, in the present system bothwriting on the image screen of the cathode ray tube (CRT) andillumination of the screen in the fluorescent mode are effected byelectron beams. The write function requires a high beam exposure and theluminescent function a lower beam exposure which repeatedly illuminatesthe screen.

Accordingly, an object of the present invention is to provide a novelsystem for effecting background fluorescent illumination of a cathoderay tube (CRT) image screen that is both cathodochromic andcathodoluminescent.

Another object of the present invention is to provide a CRT system inwhich the screen is both cathodochromic and cathodoluminescent and inwhich no ultraviolet shielding is necessary, as is required by otherillumination schemes.

These are still further objects as discussed hereinafter.

The objects of the present invention are achieved by a cathodochromiccathode-ray tube (CRT) display system comprising a CRT and associatedfocusing, deflecting and modulating electronic circuits to control theelectron beam. The CRT consists of an envelope with a faceplate, animage screen and electron beam producing means including one or moreelectron guns. The image screen is made of a material which is bothcathodochromic and cathodoluminescent such as germanium-doped, sodalite,N21 Al (Ge Si 0 ,2- (l-z)NaX, wherein X is Br, Cl, 1, OH and mixturesthereof, y is the atomic percent of germanium and 0.003 y 0.30, and z isthe fraction of NaX vacancies. The electron guns are used to provide thefunctions of writing on the image screen and exciting the screenfluorescence. In operation, information is written on the image screenby a modulated electron beam which pro vides sufi'icient exposure fordark coloration of the screen material. In low ambient light, theinformation is read by illuminating the entire screen with electronswhich are capable of exciting luminescence but are unable to causesignificant coloration. Since the luminescence is greatly reduced incolored areas, a very high contrast image is achieved and appears asdark indicia on a bright green background.

The present method of fluorescence excitation offers at least twoadvantages over methods in which ultraviolet illumination of the imagescreen is employed as the excitation means. First, it is not necessaryto provide viewer protection from harmful ultraviolet radiation and,second, the CRT fabrication can be much simpler and thus less expensive.

The invention is hereinafter discussed with reference to theaccompanying drawing in which:

FIG. 1 is a side section viewing a cathode ray tube (CRT) having animage screen that is both cathodochromic and cathodoluminescent andhaving a transparent conductive coating on the faceplate of the CRTbetween said faceplate and the image screen thereof;

FIG. 2 is a partial section view of a modification of the CRT of FIG. 1and shows a tube in which the image screen is sandwiched between aninside conductive coating and the faceplate of the CRT; and

FIG. 3 is a schematic circuit diagram in block diagram form showing aCRT and circuitry operable to perform the present teaching.

Turning now to FIG. 1, the cathodochromic cathode ray tube (CRT) shownat 101 comprises a glass envelope 1 having a transparent faceplate 2 onthe inner surface of which there is deposited a sandwich structureconsisting of a transparent conductive layer 3 and a cathodochromicimage screen 4. The anode consists of the thin conductive layer 3deposited directly upon the inner surface of the faceplate 2 andextending along the inner side walls of the envelope 1 to makeelectrical contact with an Aquadag (trademark of Acheson ColloidsCompany, a division of Acheson Industries, Inc, Port Huron, Mich.) oraluminum coating 9 which extends along the side walls 10 of the envelopeto an electron gun 5. The electron gun 5 acts to write upon thecathodochromic image screen 4 as well as to illuminate the screen in thefluorescent mode, when the display is to be viewed in low ambient light,as hereinafter dis cussed. An alternate method of illuminating thescreen in the fluorescent mode is the use of one or more offaxiselectron flood guns 11 and 11 which flood the entire screen withelectrons of sufficient energy to excite the cathodoluminescence. Theimage is viewed in high ambient light by transmitting viewing light,provided by a bulb 12, through the screen toward the viewer.

The CRT anode, comprising the coatings 3 and 9 in FIG. 1 may be replacedby an all aluminum anode in some cases. FIG. 2 shows the screenstructure in this case in which the image screen 4 is deposited directlyon the faceplate 2 and between the faceplate and an aluminum coating 13.The aluminum coating covers the entire back surface of the image screenand extends along the side walls of the envelope. One advantage of thealuminum film is that it reflects all fluorescent light that is beingemitted away from viewer back toward the viewer thus increasing theeffective light output. In this case, the image is read under reflectinglight in high ambient light conditions rather than transmitted light asshown in FIG. 1.

The cathodochromic and luminescent screen material may be sensitizedgermanium doped, sodalite, Na- ;Al (Ge ,,Si, O '2(1-z)NaX, wherein X ischosen from the group consisting essentially of Br, Cl, I, OH andmixtures thereof, 0.003 y 0.30 and z is the fraction of NaX vacancies.(See the application entitled Cathode Ray Tube Whose Image Screen isBoth Cathodochromic and Fluorescent and the Material for the Screen) Theimage screen thus comprises a material that has a coloration or F-center(i.e., the cathodochromic characteristic) as well as a luminescent orfluorescent center (i.e., the cathodoluminescent characteristic). Asnoted elsewhere herein, writing is effected by use of a high intensityelectron beam which creates the coloration or F-center to produce darkindicia on the screen, the necessary contrast to enhance the indicia inlow ambient light being provided by subjecting the image screen to a lowintensity electron beam that excites the luminescent center. The screencoloration for the sensitized germanium doped sodalite just described isdark indicia with a bright green background. The image-screen materialis such that the F-center absorption band occurs very close to theluminescent center emission band so that much of the fluorescencecreated within the colored portions of the image screen is reabsorbed toprovide the high-contrast ratios discussed in said application Ser. No.456,961.

The block diagram cathodochromic CRT display system 102 shown in FIG. 3implements the present inventive concepts. The cathodochromic CRT 101(the flood-guns 11 and 11' are omitted) is shown with a magneticfocusing coil 12A and a deflection coil 12B. In this case, focusing theelectron beam is accomplished by passing a constant current provided bya constant current supply 14, through the magnetic focusing coil 12A.Focusing can also be accomplished electrostatically, as is known in theart. The electron beam is accelerated toward the image screen by a highvoltage, usually 20 kv for writing, provided by a power supply 15 whichalso provides the appropriate voltage for the electron gun 5 in FIG. 1.Information is written on the image screen by a combination ofmodulation and deflection of the electron beam. Modulation circuits l6send a signal to a blanking amplifier 17 which, in turn, varies thecathode voltage and thus the intensity of the electron beam from zero tofull scale, usually 500p.a for writing, as read on an ammeter 18. Thesecircuits are protected from internal CRT arcing by an are protectioncircuit 19. Trigger circuits in the element labeled l6 trigger a sweepgenerator 20 which provides the appropriate voltage signals forpositioning the electron beam. These voltage signals are thentransformed to current waveforms by a deflection amplifier 21 and thecurrents, one for each axis x and y, pass through the deflection coil12B, thus positioning the electron beam on the image screen. Deflectionmay also be accomplished electrostatically. For raster scan operation,the electron beam moves horizontally across the screen and verticallydown the screen, such that the entire screen area is encompassed. As thebeam sweeps, it is modulated on and off in such a manner to write thedesired information. The sweep rate of the beam must be sufficientlyslow to provide adequate exposure for dark coloration. Once informationis written on the screen, the electron beam is again scanned, in araster format, over the entire screen. In this case, the beam is notmodulated, except possibly during retrace, and the sweep rate issufficiently fast that little or no coloration occurs this oftenrequires reducing both the electron beam current and acceleratingvoltage below the values used for writing in addition to increasing thesweep rate. However, the exposure is such that cathodoluminescentemission does occur and, as the beam sweeps repeatedly over the screen,the image appears as dark indicia on a light background. If the screenmaterial is Na Al (Ge,,Si O -2( lz)NaX, wherein X is Br, Cl, I, OH andmixtures thereof, 0.003 y 0.30, and 0 z l, the background emission isbright green at approximately 5250A. If electron flood guns, 11 and/or11 in FIG. 1 are used to illuminate the screen to excite thecathodoluminescence, the information is again written on the screen asdescribed above in relation to FIG. 3. The information is viewed in lowambient light by placing the appropriate voltage on the electron floodguns such that the entire screen area is showered with electrons whichare capable of exciting cathodoluminescence. This method allows theinformation to be read as it is being written whereas in the previouscase this was not possible.

Modifications of the invention herein described will occur to personsskilled in the art and all such modifications are deemed to be withinthe spirit and scope of the invention as defined by the appended claims.

What is claimed is:

l. A cathode ray tube that comprises: an envelope having a faceplate; animage screen in said envelope, said image screen comprising a materialthat has a coloration or F-center as well as a luminescent orfluorescent center so that said material is cathodochromic and is alsocathodoluminescent, the cathodochromic coloration lifetime being atleast 1 month, the coloration or F-center absorption band of saidmaterial occurring very close to the emission band of the luminescent orfluorescent center; and means for producing an electron beam for writingon the image screen by exciting the coloration or F-center and forexciting the cathodo luminescence in the image screen by exciting theluminescent or fluorescent center.

2. A cathode ray tube as claimed in claim 1 in which the means forproducing an electron beam includes an electron gun, an anode and beamfocusing and deflec tion means and in which said deflection means isadapted to provide at least two different raster scan rates, the slowerrate serving to write upon the image Ill screen and the faster rateserving to excite cathodoluminescence.

3. A cathode ray tube as claimed in claim 2 in which the faster scanrate repeats to expose the screen to the electron beam for an extendedtime period, such that the luminescence remains visible.

4. A cathode ray tube as claimed in claim 3 in which the fast scan rateis about 1/30 of a second per frame.

5. A cathode ray tube as claimed in claim 1 in which the means toproduce an electron beam includes an electron gun, an anode and focusingand deflection means and which further includes means to change theelectron beam intensity from one to the other of at least two intensitylevels, the lower intensity level serving to excite cathodoluminescenceand the high intensity level serving to write on the image screen.

6. A cathode ray tube as claimed in claim 1 in which the means toproduce an electron beam includes a first electron gun that serves towrite on the screen and a second electron gun to excitecathodoluminescence.

7. A cathode ray tube as claimed in claim 6 which includes at least twoelectron guns to excite cathodoluminescence.

8. A cathode ray tube as claimed in claim 7 in which the electron gunsthat excite cathodoluminescence are electron flood guns.

9. A cathode ray tube as claimed in claim 1 in which said material is NaAIAGe Si J O 2( lz)NaX wherein X is chosen from the group consistingessentially of chlorine, bromine, OH and iodine and mixtures thereof, yvaries from about 0.003 to 0.30, and 0 z 1.

10. A cathode ray tube having an image screen comprising a material thathas a coloration or F-center as well as a luminescent or fluorescentcenter, so that the screen is both cathodochromic andcathodoluminescent, and having electron beam means both to write on theimage screen by exciting the coloration or F-center and to excitecathodoluminescence in the image screen by exciting the luminescent orfluorescent center, the coloration or F-center absorption band of saidmaterial occurring very close to the emission band of the luminescent orfluorescent center so that much of the fluorescence created Within thecolored portions of the image screen is reabsorbed to enhance thecontrast

1. A cathode ray tube that comprises: an envelope having a faceplate; animage screen in said envelope, said image screen comprising a materialthat has a coloration or F-center as well as a luminescent orfluorescent center so that said material is cathodochromic and is alsocathodoluminescent, the cathodochromic coloration lifetime being atleast 1 month, the coloration or Fcenter absorption band of saidmaterial occurring very close to the emission band of the luminescent orfluorescent center; and means for producing an electron beam for writingon the image screen by exciting the coloration or F-center and forexciting the cathodoluminescence in the image screen by exciting theluminescent or fluorescent center.
 2. A cathode ray tube as claimed inclaim 1 in which the means for producing an electron beam includes anelectron gun, an anode and beam focusing and deflection means and inwhich said deflection means is adapted to provide at least two differentraster scan rates, the slower rate serving to write upon the imagescreen and the faster rate serving to excite cathodoluminescence.
 3. Acathode ray tube as claimed in claim 2 in which the faster scan raterepeats to expose the screen to the electron beam for an extended timeperiod, such that the luminescence remains visible.
 4. A cathode raytube as claimed in claim 3 in which the fast scan rate is about 1/30 ofa second per frame.
 5. A cathode ray tube as claimed in claim 1 in whichthE means to produce an electron beam includes an electron gun, an anodeand focusing and deflection means and which further includes means tochange the electron beam intensity from one to the other of at least twointensity levels, the lower intensity level serving to excitecathodoluminescence and the high intensity level serving to write on theimage screen.
 6. A cathode ray tube as claimed in claim 1 in which themeans to produce an electron beam includes a first electron gun thatserves to write on the screen and a second electron gun to excitecathodoluminescence.
 7. A cathode ray tube as claimed in claim 6 whichincludes at least two electron guns to excite cathodoluminescence.
 8. Acathode ray tube as claimed in claim 7 in which the electron guns thatexcite cathodoluminescence are electron flood guns.
 9. A cathode raytube as claimed in claim 1 in which said material is Na6Al6(GeySi1y)6O24 . 2(1-z)NaX, wherein X is chosen from the group consistingessentially of chlorine, bromine, OH and iodine and mixtures thereof, yvaries from about 0.003 to 0.30, and 0<z<1.
 10. A cathode ray tubehaving an image screen comprising a material that has a coloration orF-center as well as a luminescent or fluorescent center, so that thescreen is both cathodochromic and cathodoluminescent, and havingelectron beam means both to write on the image screen by exciting thecoloration or F-center and to excite cathodoluminescence in the imagescreen by exciting the luminescent or fluorescent center, the colorationor F-center absorption band of said material occurring very close to theemission band of the luminescent or fluorescent center so that much ofthe fluorescence created within the colored portions of the image screenis reabsorbed to enhance the contrast ratio of the image.